As a requirement on a voice service quality becomes increasingly high in modern communications, the 3rd Generation Partnership Project (3GPP) proposes an adaptive multi-rate wideband (AMR-WB) voice codec. The AMR-WB voice codec has advantages such as a high voice reconstruction quality, a low average coding rate, and good self-adaptation, and is the first voice coding system that can be simultaneously used for wireless and wired services in the communications history. In an actual application, on a decoder side of an AMR-WB voice codec, after receiving a low band bitstream sent by an encoder, the decoder may decode the low band bitstream to obtain a low band linear prediction coefficient (LPC), and predict a high-frequency or wideband LPC coefficient by using the low band LPC coefficient. Furthermore, the decoder may use random noise as a high band excitation signal, and synthesize a high band signal by using the high band or wideband LPC coefficient and the high band excitation signal.
However, it is found in practice that, although the high band signal may be synthesized by using the random noise that is used as the high band excitation signal and the high band or wideband LPC coefficient, because the random noise is often much different from an original high band excitation signal, performance of the high band excitation signal is relatively poor, which ultimately affects performance of the synthesized high band signal.